The Macintosh was Apple's first attempt at a home market computer. The second of Apple's computers to have a [wiki]Graphical User Interface[/wiki] (GUI) the Macintosh was a very user friendly and for the time remarkably cost-effective computer compared to the market-leading IBM PC in a comparable configuration, though significantly more expensive for its features than popular 8 bit systems of the time, such as the Kaypro II or a 128K Apple II system.
[wiki="File:Mac128k.jpg"]200px|thumb|top left|A mac 128k[/wiki]

The Mac 128k is so-called this due to it's 128 [wiki]kilobytes[/wiki] of [wiki]RAM[/wiki]. The 128k had a Motorola 68000 [wiki]processor[/wiki] running at a speed of 7.83 [wiki]mHZ[/wiki]. The 128k had an internal single sided, Single Density 400k Floppy Drive. The monitor was a 9 inch [wiki]monochrome[/wiki] [wiki]Cathode Ray Tube[/wiki] Black and White display.
There were two models of 128K Macintosh. The original, with the Macintosh badge, some of which were shipped badged as Macintosh 128K after the [wiki="Fat Mac"]512KB model[/wiki] was released. The later model hadd a logic board design similar to the 512KB model, to reduce production costs, though it was still sold with only 128KB as an entry level model. Neither model was user upgradeable.
Of general interest

The Mac 128K was originally released simply as the "Macintosh". When the 512KB [wiki]Fat Mac[/wiki] appeared on the market, the original model was rebadged as the Macintosh 128K.
The Mac 128k can be seen many times in popular culture. For example the Mac 128k can be seen in many episodes of the popular television series Seinfeld on a desk which is usually in the background. The 128k sold for $2500 and had no internal expansion. The 128k had the names of the developers engraved on the inside of the case which required special factory tools to open. The 128k was originally marketed as a business machine although it eventually became a home/office machine. The episode of [wiki]The Computer Chronicles[/wiki] which covered the Macintosh 128k is one of the most sought after episodes of the popular series.
General Problems

The Mac 128k had the majority of its components soldered to the board making them impossible to replace if they failed. The case requires special tools to open which may not be readily available and in some cases may result in the breaking of the case or computer if attempted without these tools. Though hardware projects to increase memory or add additional I/O interfaces to the Macintosh were published in some magazines, the technical nature of these projects (involving modifications to the logic board and soldering piggyback chips onto the installed ICs on the logic board) meant that there was no possibility of upgrade for most Mac users.
After the release of the Mac 512Ke, Apple offered an upgrade for the 128K that would replace the logic board and a portion of the case for the price of $1000, increasing memory to 512K and allowing the use of the 800K floppy disk drive of the 512Ke model. Later, a similar program was offered providing a Mac Plus logic board.
The amount of memory used by the operating system and bitmap graphics left less than 48KB available for user applications, less than was commonly available on the 8 bit platforms of the time. Many developers were unable to port their applications to the Mac until the 512KB versions were released.
Prerelease Software Development

During development of the Macintosh, outside software developers were provided Lisa computers to allow them to develop software for or port software to the forthcoming Macintosh. A series of software emulations of the Macintosh's system software and Finder were released during this period with varying degrees of fidelity to the actual Macintosh. These later became the basis for the 7/7 package used by the Lisa/Macintosh XL to provide Macintosh software compatibility for that platform.
As the Lisa had significantly more memory than the Macintosh (512KB to 2MB), the most common reason for software developed under the emulation failing when run on the actual Mac was lack of available memory. The actual amount of memory promised for applications continued to fall as the Mac neared completion to well below 64KB. The result was that many titles originally intended for release for the original Mac were withheld until the release of the 512KB model (already planned at the time of the original release) or were dropped entirely.